Individuals who lack or have severely diminished mitochondrial aldehyde dehydrogenase-2 (ALDH2) activity are at very low risk in developing alcoholism, since they cannot drink a large amount of alcohol. The deficiency is due to the atypical ALDH2 gene existing in such individuals at heterozygous ALDH2(1)/ALDH2(2) or homozygous ALDHs(2)/ALDH2(2) status. Alcoholism may be cured by introducing the nucleotide construct containing the ALDH2(2) into patients. This possibly can be tested in animal models. Mouse strain(s) associated with a high alcohol preference (such as C57BL/6J) can be changed to low alcohol preference by genetically suppressing the activity of mitochondrial ALDH. The following two studies are proposed: 1) Non-homologous integration of a mutant gene: The procedures are injections of a mutant ALDH construct(s), which is equivalent to human atypical ALDH2(2) gene, into fertilized eggs, and subsequent transplantation of the treated eggs into pseudo-pregnant mice. Transgenic mice thus produced are a sort of human heterozygous ALDH2(1)/ALDH2(2) status, and are expected to exhibit a diminished ALDH activity and a low alcohol preference. 2) Knockout the mouse mitochondrial ALDH gene targeting; The procedures include; a) transfection of mouse embryonic stem cells with a recombinant construct containing a modified ALDH gene fragment and a marker(s); b) inject transfected cells into blastocysts; c) transfer the blastocysts into pseudo-pregnant mice; and d) breeding of chimeratic offsprings to produce homozygous and heterozygous mutant strains. During the course of the experiment, incorporation of artificial mutant genes into animals is monitored by PCR-mediated DNA hybridization. Liver mitochondrial ALDH activity and alcohol preference in the original strain and the artificially produced mutant strains will be compared to verify the expectation.